Field level variability in topography and soil quality: implications on dryland cereal production in the Central Great Plains of North America.

Producers now have the capacity to obtain a wealth of tractor-based yield data and topographic information. In addition, technologies such as Veris-EC allow for the rapid acquisition of large amounts of soil data across fields. However, there is currently no clear guidelines about how to use this data to inform field management decisions in dryland grain production. This is because of the lack of a fact-based consensus about the development of specific recommendations based on the different field data layers. In this project, we are studying a replicated set of field-sized experimental plots that each have considerable unevenness in grain yield. We aim to explore and document the relationship between crop productivity and soil variability under natural climate fluctuations at the field scale. We hypothesize that elevation gradients within each field in part account for differences in soil quality, profile water storage, and water movement, all of which determine grain yield variations across the field. A necessary first step in this effort is to document geospatial variability in grain yields and soil parameters and identify soil characteristics that are associated with low and high productivity areas within a field. Once those associations are recognized and measured, then we will be able to modify management practices to exploit of those differences. We measured wheat, maize and millet yields in 18 different fields, and also measured a suite of soil parameters using a grid sampling scheme within each field. We also obtained detailed elevation data and electrical conductivity readings. Using calculated data from kriged interpolations we carried out correlation analyses between the different data sets. While elevation was often correlated to grain yields, other soil attributes like pH, C content, texture, and available P showed inconsistent results. With the first two years of data, it is becoming evident that topography is more important than soil factors in determining the spatial variation in crop yields. We believe that these rather small variations in elevation are associated with hydrologic phenomena that are in the end the most directly pertinent to crop performance in this semiarid climate .